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In this work it is established that a close relationship exists between the feeding of rancid feed (containing high amounts of lipid peroxides and a, ^-unsaturated aldehydes) and lipoid liver degeneration (LLD) in fish. The main feature of the disease is a large accumulation of ceroid in hepatocytes, giving positive histochemical staining reactions with a number of selective stains. Tissues also reacted strongly for lipid peroxides and fluoresced a bright yellow-green at 450 nm. This is the first report on the ultrastructure of ceroid in LLD. The accumulations consist of bodies containing cholesterol or cholesterol ester crystals and inclusions with membranous profiles. The latter type of inclusion is considered to be representative of ceroid.

Lymphosarcomas occur in several species of bony fishes and are common in the northem pike, Esox lucius L. In a recent review on tumours in fishes, Mawdesley-Thomas (1975) listed the occurrence of lymphosarcomas in five species of salmonids. The only case in the Atlantic salmon was reported by Haddow& Blake (1933). In that case the tumour seemed to originate from the kidney.This report describes lymphosarcomas in the muscular tissue of a female Atlantic salmon Salmo salar L. The five year-old fish was caught in good physical condition in the Vefsenfjord in the northern part of Norway. It was brought to the laboratory because of obvious external abnormalities. Gross findingsAltogether seven neoplastic lesions were found scattered in the trunk musculature. Five of these tumours could be traced from swellings on the surface of the fish body. On the right side of the body the tumours were located as follows (Fig, 1): (1) at the outer edge of the mandibular, (2) close behind the operculum below the midline, (3) just in front of and laterally to the dorsal fin, (4) at the base of the tail fin, (5) between the spines of the tail fin. On the left side one tumour was located closely behind the adipose fin. Two tumours were found in the trunk musculature ventral to the dorsal fin. The tumours ranged in size from 3 to 10 cm in length and from 2 to 4 cm in height.The tumour behind the operculum was soft and ulcerated, while the bulging tissue of the other tumours was firm, and they were all covered by intact, moveable scales and skin. The cut surface of slices taken sagittally through the centre of the tumours revealed a pale, yellowish-grey homogeneous tissue separated from the surrounding muscular structures.

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